Architecture of fully differential circuits is commonly adopted in a switching amplifier. FIG. 1(a) shows a schematic drawing of a switching amplifier 10 of the background art. The amplifier 10 comprises a first half circuit 11, a second half circuit 12 and a reference wave generator 13. The circuit 11 and 12 both comprise a modulator and a driver circuit. The reference wave generator 13 is connected to the same input end of a modulator 111 and modulator 121. Signals VIN11 and VIN12 are inputted to the other end of the modulator 111 and modulator 121, respectively. The signals VIN11 and VIN12 are a differential pair, which have opposite AC signals on the same DC level, wherein the DC level is the same as a reference wave 131. Signals VOUT11a and VOUT12a are output signals of modulator 111 and 121, respectively. The modulator 111 and 121 switch when the input signals VIN11 and VIN12 become larger or smaller than the reference signal 131, and then signals VOUT11a and VOUT12a are generated and inputted to driver circuits 112 and 122, respectively. The driver circuits 112 and 122 have constant magnification. Signals VOUT11 and VOUT12 are output signals of driver circuits 112 and 122, respectively. Signals VOUT11 and VOUT12 are inputted to two ends of a load circuit 15, respectively. Thus, a voltage difference VOUT1 is a differential output signal and equal to a value of VOUT11-VOUT12.
As a common reference wave of the first half circuit 11 and second half circuit 12, the reference wave 131 is generated by the wave generator 13. While the first half circuit 11 switches, it may interfere with the second half circuit 12 through the reference wave 131, and lead to an early or late switching of the second half circuit 12. High-frequency switching signals also interfere with switching of the second half circuit 12 through the parasitic capacitance or common power circuit or ground circuit. For example, As shown in FIG. 1(b), while VOUT11 switches at t1, VOUT12 switches at t1 instead of t2, which is due to interference as mentioned above. Similarly, while VOUT12 switches at t3, VOUT11 switches at t3 instead of t4. Therefore, output signals of driver circuit 112 and 122 are the same, i.e., VOUT11 and VOUT12 overlap, and the differential output signal VOUT1 disappears, which is one of the distortion sources of the output signal. If an input signal is small, output error caused by interference is relatively large. Thus, a nonlinear relationship between the input and output signal is generated